Field of the Invention
The present invention relates to an electrostrictive element.
Description of the Related Art
It is known that, when electrodes are connected with both front and back surfaces of a dielectric film composed of an elastomer and voltage is applied, the dielectric film is subjected to compressive force by the Maxwell stress (piezoelectric inverse effect) from the interfacial polarization due to electrostatic force, contracts in the thickness direction and expands in the lateral direction (the direction orthogonal to the thickness direction). In recent years, there has been considered an electrostrictive element that comprises a dielectric film and electrodes and that is driven by this principle.
As such an electrostrictive element, there has been proposed a dielectric-based drive device comprising a dielectric film that is composed of an elastomer, film electrodes that are formed inside the peripheral edges of both front and back surfaces of the dielectric film and that can expand and contract so as to follow the expansion and contraction of the dielectric film, a rim type frame that is provided on the peripheral edge of one surface of the dielectric film and that keeps the dielectric film in an expansion state, current collectors that are connected with the peripheral edges of the film electrodes (see Japanese Patent Laid-Open 2003-174205, for example). The current collectors, each of which has one end connected with the peripheral edge of the film electrode and has another end extend outside the dielectric film, supply electricity to the film electrodes.
In the electrostrictive element, when a positive or negative voltage is applied to the film electrodes through the current collectors, the dielectric film contracts in the thickness direction and expands in the lateral direction. However, since the peripheral edge of the dielectric film is kept by the rim type frame, the dielectric film expands inward due to the restriction of the outward expansion, and projects to the side of one surface so as to have a nearly mountain shape as a whole. Then, the film electrodes expand so as to follow the behavior of the dielectric film for the expansion, and are transformed into a nearly mountain shape.
Thereafter, by the stop of the application, the expanded dielectric film is restored to a nearly original shape, and the expanded film electrodes are restored to a nearly original shape so as to follow the behavior of the dielectric film for the restoration.
However, the current collector extends outside the film electrode and contacts with the surface of the dielectric film composed of an elastomer. Therefore, in the case where a metal plate of copper or the like is used as the current collector, disadvantageously, when the dielectric film expands and contracts repeatedly, the surface of the dielectric film is damaged by corner portions of the plate-shaped current collector, and there is a fear that the dielectric film is broken from the portions.
Further, in the electrostrictive element, when the film electrode expands with the expansion of the dielectric film, a load is given to the current collector connected with the peripheral edge of the film electrode, and there is a fear that the current collector or the connection portion between the current collector and the film electrode is broken.
The present invention has an object to solve such disadvantages and to provide an electrostrictive element that can prevent the breakage.